SYDNEY, July 23 (Reuters) - An Australian Islamist preacher who has expressed support for militants fighting in Syria and Iraq will face police surveillance but no criminal charges in Australia, where he arrived on Wednesday after being deported from the Philippines.

Melbourne-born Musa Cerantonio, who has been a vocal supporter of the Islamic State militant group and its leader, Abu Bakr Al-Baghdadi, was deported due to "invalid travel documentation", the Australian Federal Police (AFP) said.

This month, Cerantonio, who converted to Islam from Catholicism at 17, said he would be travelling to fight in Syria, the Australian Broadcasting Corporation (ABC) reported, although Australian police said he never got there.

"Mr Cerantonio's known social media postings are considered offensive and disturbing, however, have been assessed as not breaching Australian law to this point," the AFP said in a statement.

"The AFP will continue to monitor and assess this material for any breaches of Australian law into the future."

Cerantonio has emerged as perhaps the most prominent of a young generation of radical Australian Islamists, more than 100 of whom are estimated by law enforcement agencies to have travelled to fight in Iraq and Syria.

Australia has raised the alarm about the number of its citizens believed to be fighting alongside insurgents overseas, including an Australian suicide bomber who killed three people in Baghdad this month

That has added to concern about radicalised fighters committing terrorist acts when they return home, a threat the government has used to justify a package of major new intelligence legislation.

Last week, Attorney General George Brandis announced sweeping national security reforms that would make it easier to track Australian citizens believed to have fought overseas both while they were abroad and after they returned home. (Editing by Robert Birsel)